1. Field of the Invention
This invention relates to an arc shield for use in projection welding, which encloses the electric arc therein.
2. Description of the Related Art
In the architectural art, a metal stud is often used in projection welding to couple a steel member or a plurality of steel members with a concrete layer. Referring to FIG. 1, a metal stud (1) is welded to an H-shaped steel member (3) and is embedded within a concrete layer (5). Referring to FIG. 2, in order to weld the lower end of the vertical cylindrical stem (1A) of the stud (1) to the upper surface of the top plate of the steel member (3), a generally semicircular metal filler (11) is attached to the lower end surface of the stem (1A) of the stud (1). A welding gun (2) holds the horizontal head (1B). When an electric current is applied to the stud (1) from the welding gun (2), an electric arc is created between the stud (1) and the steel member (3). Accordingly, molten weld metal (12) is produced between the stud (1) and the steel member (3). Solification of the molten weld metal (12) welds the stud (1) to the steel member (3).
Referring to FIG. 3, in order to weld a plurality of steel members (3') (only one is shown) to a concrete layer (not shown), a metal coupling plate (6) is provided so as to weld the steel members (3') thereto. The coupling plate (6) is coupled with the concrete layer by a stud (1') and a welding gun (2') in the same manner as the steel member (3) of FIG. 1.
The above-mentioned welding process suffers from the following disadvantages:
(1) If no arc shield is used, the electric arc may damage the eyes of the operator;
(2) When the operator holds an arc shield with one hand, it is difficult with one-hand operation to accurately position the stud on the steel member. Furthermore, it is time-consuming to perform this one-hand operation.
(3) Because the molten weld metal is exposed to the atmosphere during welding, dust may enter therein, thus forming bubbles in the solidified weld metal. The bubbles reduce the tensile strength of the solidified weld metal.